This invention relates to centrifugal separators and, more particularly, to the improvement in a method of installing the frustoconical screen in a vertical centrifugal separator so as to achieve optimal rounding of the screen.
Centrifugal separators are widely used in a variety of industrial processes requiring material separation. A variety of centrifugal separators, both vertical and horizontal, are disclosed in the following U.S. Pat. Nos.: U.S. Pat. No. 4,135,659 to Derton et al.; U.S. Pat. No. 4,922,625 to Farmer; U.S. Pat. No. 1,903,795 to Rigler; U.S. Pat. No. 1,664,769 to Chance; U.S. Pat. No. 1,334,023 to Elmor; U.S. Pat. No. 2,752,043 to Vanriel; U.S. Pat. No. 2,727,631 to Pate; U.S. Pat. No. 2,370,353 to Howe; U.S. Pat. No. 3,361,264 to Quetsch; U.S. Pat. No. 3,315,810 to Humphrey et al.; U.S. Pat. No. 3,289,843 to Nyrop; U.S. Pat. No. 3,074,842 to Strong; U.S. Pat. No. 3,837,913 to Hillebrand et al.; U.S. Pat. No. 4,157,966 to Hassall; U.S. Pat. No. 3,411,631 to Elsken et al.; U.S. Pat. No. 4,961,722 to Taylor et al.; U.S. Pat. No. 3,418,097 to Dudley et al.; and U.S. Pat. No. 3,438,501 Oyen.
Centrifugal separators are generally constructed having vertical drive mechanism including a drive shaft. A flight assembly is attached to the drive shaft and rotatably driven. A frustoconical screen assembly, which includes a rotor, is also attached to the drive shaft. The screen rotor is driven at a separate speed as the flight assembly. The perforated frustoconical screen is positioned outwardly of the flight assembly. The material to be separated is placed in the centrifugal separator between the flight assembly and the screen and, in this area, the separation occurs.
Typically, material is fed into the top of the separator and placed in the area between the flight assembly and the screen but in contact with the flight. As the flight and the screen assembly spin at different rates, solid material is retained near the center of the assembly on the flight side of the screen while free liquids are slung off, by centrifugal force, through the screen to an outside area of the separator. The liquids are then collected in a collecting means and directed to a drain outlet. Solid materials fall under the force of gravity to the bottom of the separator where they are discharged and collected.
As is obvious from this general description of the operation of a centrifugal separator, the clearance between the flight and the frustoconical screen surface is critical to the efficient operation of the centrifugal separator. If the screen does not become rounded during installation, there can be large clearances between the flight and screen in some areas and the flight may actually touch the screen in other areas. Large gaps decrease the efficiency of the machine. Touching of the screen by the flight causes premature screen wear.
Generally, in assembly methods of the prior art, the frustoconical screen is placed around the top of the flight and pushed down over the flight into position. Some centrifugal separators have a basket frame to seat the screen. In the centrifugal separators employing the basket frame, the screen is pushed or forced down over the flight into the basket. The lower portion of the screen is then attached or clamped to the lower portion of the basket to secure it in place.
If the screen is stiff or rigid, it is difficult to achieve proper rounding of the screen when pushing it into position within the basket. Pushing the screen bends the screen toward the flight and decreases clearance in some areas. Furthermore, bar screens, for example, those manufactured by Bixby-Zimmer, Galesburg, Ill., and Johnson Filtration, St. Paul, Minn., are even more rigid and difficult to round into shape.